1. Field of the Invention
This invention relates to room temperature-curable polyorganosiloxane compositions. More particularly, this invention relates to such room temperature-curable polyorganosiloxane compositions that exhibit improved water resistance during the initial stages of curing relative to prior art compositions.
2. Description of the Prior Art
The use of organosilicon compounds containing two amide groups in combination with organosilicon compounds containing 3 or more amide or aminoxy groups in room temperature vulcanizable compositions containing a hydroxyl-terminated polyorganosiloxane has been disclosed in the prior art. By varying the ratio of these difunctional and polyfunctional curing agents, it is possible to obtain a range of properties in the cured product ranging from low modulus and high elongation to high moldulus and low elongation. Low modulus-high elongation materials are widely used as construction sealants due to the superior resistance of these materials to weather and fatigue.
Room temperature vulcanizable (RTV) compositions typically contain fillers such as silica and calcium carbonate to improve the physical properties or to impart certain characteristics, such as paintability, to the cured products. Paintable RTV compositions containing hydroxyl endblocked polydiorganosiloxanes, acyloxysilanes, tin carboxylate catalysts and a finely divided, accicular form of calcium carbonate are disclosed in U.S. Pat. No. 3,957,714, which issued to Clark and Johnson on May 18, 1976, and in U.S. Pat. Nos. 4,247,445 and 4,293,616, which issued to Smith, et al. on Jan. 27 and Oct. 6, 1981, respectively.
None of the aforementioned references concerning the use of calcium carbonate in RTV polyorganosiloxane compositions disclose the susceptability of incompletely cured RTV polyorganosiloxane compositions containing calcium carbonate as a filler to undergo cracking, flow out, inhibition of curing and/or loss of adhesion to an underlying substrate in the presence of water.
One objective of this invention is to provide moisture curable calcium carbonate filled RTV polyorganosiloxane compositions which are more water resistant during curing than prior art compositions.
A second objective of this invention is to provide a method for increasing the water resistance of incompletely cured RTV polyorganosiloxane compositions containing calcium carbonate as a filler without adversely affecting other properties of the cured compositions, such as adhesion.